This study investigated the influence of attending public, Catholic, or independent secondary schools on students' course taking in mathematics, using data on 3,374 high school graduates of 184 urban and suburban high schools from the High School Effectiveness Supplement to the National Education Longitudinal Study of 1988. With hierarchical linear modeling methods and accounting for factors associated with selection into schools in different sectors, the authors found that the private school students took more advanced mathematics courses than did the public school students. However, after controlling for additional differences in selectivity between the two types of private schools, they found that Catholic schools influence their students' course-taking behaviors especially strongly and that the social distribution of course taking is especially equitable in Catholic schools.